Some Muslim scholars writing under the Almoravids were favourable to a hardening of the conditions under which Jews and Christians lived in their societies. Concern about the sincerity of belief of recent converts does not seem to have produced similar anxiety in earlier times. After all, Muslims had been at the beginning a minority surrounded by a majority of Christians and by Jewish communities of different sizes. The demographic balance had precisely changed thanks to the process of conversion to Islam, that is, the process by which Christians, Jews and others abandoned their previous religious allegiances and became Muslims, a process which was mostly voluntary in the case of the monotheists. Historical sources provide abundant information about the fact that the Almohads considered the mosques they encountered in the conquered territories to be polluted and therefore in need of purification.